(1) Field of Invention
This invention is directed to novel highly cross-linked cation-exchange polymers derived from water soluble amide monomers and an in situ cross-linking reaction in an aqueous solvent to produce the water insoluble polymers.
(2) Description of the Prior Art
The usual technique for the production of ion-exchange polymers involves polymerizing of a non-ionic, non-water soluble, di-ethylenic cross-linking agent, as for example, divinyl benzene with a monomer such as styrene in a non-aqueous solvent such as diethylbenzene. The resulting solid polymer, for example, in sheet or membrane form is equilibrated or washed several times with a solvent such as ethylene dichloride to remove and replace the diethyl-benzene solvent. Where cation exchange membranes are desired the membranes are then reacted with a solution of sulfur trioxide and ehylene dichloride to form the sulfonate groups which upon washing with methanol and neutralization with sodium bicarbonate gives the polymer its strongly basic ion-exchange properties. The prior art has disadvantages in that the monomers employed are water insoluble and the polymerization reaction and subsequent reaction are caried out in non-aqueous solvents; thus necessitating chemical disposal problems with the attendant loss of the organic solvents.
The present invention comprises an improvement over the methods of the prior art by providing water soluble monomers polymerized in an aqueous solvent system. Cross-linking of the polymers occurs by means of a condensation reaction between two monomers which takes place simultaneously with the polymerization; therefore, no di-ethylenic monomers are required. The resulting ion-exchange polymeric membranes have the desired high ion-exchange capacities and low electrical resistance. Additionally, the polymerization step requires shorter time periods and lower curing temperatures for a net saving in energy. Also the expense of petroleum derived solvents and the problem of their disposal is eliminated.